The invention relates to cancer therapeutic agents and methods for cancer therapy.
The following discussion of the background of the invention is merely provided to aid the reader in understanding the invention and is not admitted to describe or constitute prior art to the present invention.
Surgery, radiation therapy, and chemotherapy have been the standard accepted approaches for treatment of cancers including leukemia, solid tumors, and metastases. Immunotherapy (sometimes called biological therapy, biotherapy, or biological response modifier therapy), which uses the body's immune system, either directly or indirectly, to shrink or eradicate cancer has been studied for many years as an adjunct to conventional cancer therapy. It is believed that the human immune system is an untapped resource for cancer therapy and that effective treatment can be developed once the components of the immune system are properly harnessed. As key immunoregulatory molecules and signals of immunity are identified and prepared as therapeutic reagents, the clinical effectiveness of such reagents can be tested using well-known cancer models. Immunotherapeutic strategies include administration of vaccines, activated cells, antibodies, cytokines, chemokines, as well as small molecular inhibitors, anti-sense oligonucleotides, and gene therapy (Mocellin, et al., Cancer Immunol. & Immunother. (2002) 51: 583-595; Dy, et al., J. Clin. Oncol. (2002) 20: 2881-2894, 2002).
The growth and metastasis of tumors depends to a large extent on their capacity to evade host immune surveillance and overcome host defenses. Most tumors express antigens that can be recognized to a variable extent by the host immune system, but in many cases, the immune response is inadequate. Failure to elicit a strong activation of effector T-cells may result from the weak immunogenicity of tumor antigens or inappropriate or absent expression of co-stimulatory molecules by tumor cells. For most T-cells, proliferation and IL-2 production require a co-stimulatory signal during TCR engagement, otherwise, T-cells may enter a functionally unresponsive state, referred to as clonal anergy.
As part of the immune system, innate immunity provides an early first line defense to pathogenic organisms which is followed by antibody and cellular T cell responses characteristic of the adaptive immune system. Innate immunity is highly robust and utilizes specific cells such as macrophages, neutrophils/PMNs, dendritic cells, and NK cells which are effective in destroying and removing diseased tissues and cells (Cooper et al., BioEssays (2002) 24:319-333). Since the demonstration by Coley that tumors could be treated by intratumoral injections of pathogens (Wiemann and Stames (1994) Pharmacol. Ther. 64:529-564), investigators have wondered if the innate immune system could be harnessed for the treatment of human diseases (Ulevitch, Nature Rev. Immunol. (2004) 4:512-520). However, attempts to use the innate immune system for cancer immunotherapy have been limited in comparison to the adaptive immune system.
As described by Medzhitov and Janeway, (Current Opin. Immunol. (1997) 9:4-9) the innate immune system is directed to recognition of invariant molecular structures in pathogens that are distinct from self-antigens yet are found on a large number of infecting organisms. These microbial stimulators of innate immune responses include lipopolysaccharides and teichoic acids shared by all gram-negative and gram-positive bacteria, respectively, unmethylated CpG motifs characterized by bacterial but not mammalian DNA, double-stranded RNA as a structural signature of RNA viruses, and mannans which are conserved elements of yeast cell walls. None of these structures are encoded by host organisms and all are shared by large groups of pathogens due to their importance in structure and/or propagation of the infecting organism. Mammals have developed a set of receptors which recognize these microbial components. Unlike T- and B-cell receptors of the adaptive immune system, however, these innate system receptors are germline encoded (since they have arisen evolutionarily over time due to selection by pathogens at the population level) and are strategically expressed on cells that are the first to encounter pathogens during infection (Ozinsky, et al., PNAS (2000) 97:13766-13771).
CpG Oligodeoxynucleotides (ODNs) are synthetic oligonucleotides that are comprised of unmethylated CG dinucleotides, arranged in a specific sequence and framework known as CpG motifs (Tokunaga, et al., JNCI (1984) 72:955-962; Messina, et al, J. Immunol. (1991) 147:1759-1764; Krieg, et al, Nature (1995) 374:546-549). CpG motifs trigger the production of T-helper 1 and pro-inflammatory cytokines and stimulate the activation of professional antigen-presenting cells (APCs) including macrophages and dendritic cells (Klinman et al. PNAS (1996) 93:2879-2883). Unmethylated CpG ODNs behave as immune adjuvants which accelerate and enhance antigen-specific antibody responses and are now thought to play a large role in the effectiveness of Freund's Adjuvant and BCG (Krieg, Nature Med. (2003) 9:831-835). Recently, it was discovered that CpG ODNs interact with Toll-like receptor (TLR) 9 to trigger the maturation and functional activation of professional antigen presenting cells, B-cells, and natural killer cells (Hemmi, et al. Nature (2000) 208:740-745; Tauszig, et al, PNAS (2000) 97:10520-10525; Lawton and Ghosh Current Opin. Chem. Biol. (2003) 7:446-451). CpG ODNs are quickly internalized by immune cells, through a speculated pathway involving phophatidylinositol 3-kinases (PI3Ks), and interact with TLR9 present in endocytic vesicles (Latz, et al. Nature Immunol. (2004) 5:190-198). The resultant immune response is characterized by the production of polyreactive IgM antibodies, cytokines, and chemokines which induce T-helper 1 immunity (Lipford, et al., Eur. J. Immunol. (1997) 27:2340-2344; Weiner, J. Leukocyte Biol. (2000) 68:445-463; Stacey, et al., Curr. Topics Microbiol. Immunol. (2000) 247:41-58; Jacob, et al., J. Immunol. (1998) 161:3042-3049). The TLR9 receptor recognizes CpG ODNs with a strict bias for the chemical and conformational nature of the unmethylated CpG ODN since conjugation of an oligonucleotide and a CpG DNA at the 5′-end has been shown to reduce significantly the immunostimulatory activity of the CpG DNA. On the other hand, conjugation of an oligonucleotide and a CpG ODN at the 3′-end does not perturb or may even enhance the immunostimulatory activity of the CpG DNA (Kandimilla, et al., Bioconjug. Chem. (2002) 13:966-974).
Recently, investigators have established three classes of CpG ODNs: CpG-A, CpG-B, and CpG-C (Verthelyi, et al., J. Immunol. (2001) 166:2372-2377; Krug, et al, Eur. J. Immunol. (2001) 31:2154-2163; Rothenfusser, et al., Blood (2004) 103:2162-2169; Vollmer, et al, Eur. J. Immunol. (2004) 34:252-262). CpG-A ODNs are potent inducers of natural killer cell activation and interferon-α secretion; CpG-B ODNs predominantly elicit B-cell proliferation and plasmacytoid dendritic cells; and CpG-C ODNs have the activity of both CpG-A and CpG-B and therefore induce both NK, plasmacytoid dendritic cell, and B-cell activation. In contrast to the first two classes, CpG-C ODNs are characterized by the absence of poly-G stretches and have palidromic sequences combined with stimulatory CpG motifs (Vollmer, et al, Eur. J. Immunol. (2004) 34:252-262).
CpG ODNs have shown efficacy in mouse models as a monotherapy (Klinman, Nature Rev. Immunol. (2004) 4:249-258; Lonsdorf, et al., J. Immunol. (2003) 171:3941-3946; Ishii et al., Clin. Cancer Res. (2003) 9:6516-6522; Baines and Celis, Clin. Cancer Res. (2003) 9:2693-2700). Direct injection of CpG ODN into tumor lesions is reported to activate local dendritic cells and induces the production of IL-12 in and around the tumor. In several different tumor models, injection of CpG-B ODN led to regression of established tumors in a T-cell dependent fashion. In a B-16 melanoma model, injection of CpG-A ODNs either into the tumor or systemically led to tumor regression in an NK dependent, T-cell independent manner (Lonsdorf, et al., J. Immunol. (2003) 171:3941-3946).
CpG ODNs have shown efficacy in mouse models when administered in combination with antitumor antibodies (Wooldridge et al, Blood (1997) 89:2994-2998). Administration of CpG ODN was found to activate dramatically ADCC effector cells and induce expression of CD64. When this treatment was followed by injection of an antitumor antibody, dramatic increases in biologic activity were seen. Regression was achieved with large tumors that would not normally respond to antibody therapy alone, as well as with tumors that only express the target antigen at low concentrations.
CpG ODNs have also shown efficacy as radiotherapy enhancers. Recent results have shown that CpG ODNs are potent enhancers of tumor radioresponse and as such have potential to improve clinical radiotherapy (Milas, et al., Cancer Res. (2004) 64:5074-5077). Likewise, CpG ODN therapy has been shown to be enhanced by prior chemotherapy and as such have the potential to improve with prior drug therapy (Li and Levy, Abstract, 19th Intl. Soc. Biol. Therapy, San Francisco, (2004).
Further improvements in the design of cancer immunotherapeutic treatments are needed.